1. Field of the Invention
The invention relates to the field of wax emulsions and mixtures for addition to settable gypsum formulations and other construction and building formulations, and more particularly to the field of such mixtures and emulsions for making gypsum wallboards having low water absorption and low solids content.
2. Description of Related Art
Gypsum wallboard is used for forming interior and exterior walls of many building structures. The structure of the wallboard typically includes a gypsum composition which is generally prepared as a slurry composition, which is placed between two liners and set. Such wallboard gypsum compositions may be standard wallboard formulations or made to be water-resistant through, for example, the use of various wax emulsions. Some of the more common commercial water-resistant wax emulsions involve use of particular wax components (which may include a single wax, or more typically, a blend of waxes), saponifying agent(s), emulsifier(s), stabilizer(s) and other additives.
Of growing importance in the wallboard industry is the ever-increasing cost of manufacture of wallboard with respect to the rising cost of formulation components as well as increasing energy costs. For example, it is known in the art that manufacturing methods for formation of building products like gypsum wallboard that use emulsions in formation of the finished products, typically require a drying step or steps that consume energy. Thus, it would be beneficial to manufacture gypsum wallboard (standard and water-resistant) if the drying energy could be reduced for cost savings, particularly when energy demands are growing for manufacturers. Components, time and steps required in manufacture are also a concern, as is the quality of the resulting wallboard.
With respect to the manufacture of water-resistant wallboards, U.S. Pat. No. 5,437,722 describes a water-resistant gypsum composition and wax emulsion therefor, which includes a paraffin hydrocarbon having a melting point of about 40° C. to 80° C., about 1 to 200 parts by weight montan wax per 100 parts of the paraffin hydrocarbon, and about 1 to 50 parts by weight polyvinyl alcohol per 100 parts of the paraffin hydrocarbon. The use of montan wax in the wax emulsion for water-resistant wallboard has been very effective and provides excellent performance. Other water-resistant formulations based on natural waxes other than montan (such as carnauba, bees wax or colophonium resin) and/or synthetic waxes (such as Fischer-Tropsch wax) have been used as well as alternative water-resistant wax formulations. Most such formulations provide good water-resistance in gypsum wallboard formulations.
Synthetic and natural waxes as noted above are used in the building products and gypsum wallboard industries for waterproofing and in oriented strand board. Among such natural waxes used in the building products industry, particularly for water-resistant gypsum wallboard, montan wax as noted above is prevalent. Montan wax is a lignite-wax, including chemical components formed of long chain alkyl acids and alkyl esters having chain lengths of about 24 to 30 carbons. In addition, natural montan includes resin acids, polyterpenes and some alcohol, ketone and other hydrocarbons such that it is not a “pure” wax. The saponification number of montan, which is a saponifiable wax, is about 92 and its melting point is about 80° C. Montan wax while highly effective has its drawbacks in that it is not always sufficiently pure and as a natural wax, tends to have some inconsistencies in formulation and more importantly, is available only in limited supply from a natural source which is generated primarily in Germany, such that the wax is becoming more expensive and obtaining adequate supply is becoming an issue for manufacturers of such wax emulsions.
Further, while strong water-resistance can be achieved, it would be desirable to achieve good water resistance properties in gypsum wallboard, while lowering the cost of components, reducing cost of supply and/or manufacturing costs by providing for lower solids content in the additive emulsion and improving slurry viscosity to avoid the need for added water during manufacturing. Further, similar emulsions are used in oriented strand board and other building and construction applications such that reduction in cost for such emulsions is desirable.
Accordingly, there is a need in the art for compositions and methods that improve the properties of gypsum wallboard or other building and construction formulations, while preferably also keeping the costs of manufacturing including reducing energy costs, reducing cost of materials, and in the case of gypsum wallboard, also improving gypsum slurry viscosity such that lower amounts of water are needed to form a suitable slurry for gypsum board formulation and thus improve drying times, while at the same time providing the same or better water resistance properties as prior waterproof or water resistant gypsum wallboard.